Cisco Systems has won the latest round against Arista Networks at a U.S. trade agency that could block importation of Arista products.

Arista violated three Cisco patents on networking technologies, Administrative Law Judge David Shaw of the U.S. International Trade Commission ruled on Tuesday. If the full Commission confirms that finding, the ruling could be bad news for Arista, a growing player in data-center networking.

Cisco sued Arista in December 2014, alleging the Silicon Valley startup violated 14 patents in the Arista EOS operating system. The legal battle continues, heading toward two possible trials in federal court as well as continuing activity at the ITC. In a blog post Tuesday, Cisco General Counsel Mark Chandler said a ruling in a second ITC investigation is expected in April.

"This notice marks the beginning of the end for Arista's systemic copying of our intellectual property," Chandler wrote.

The law judge's ruling could lead to an exclusion order that would stop Arista imports. It also sets up an ITC review process for changes Arista might make to its products so they no longer infringe Cisco's patents.

Import bans are the ITC's main weapon against companies it finds have violated patents. Technology companies commonly pursue intellectual-property claims against competitors both in the courts and at the ITC.

The ruling finds Arista violated a patent on managing router configuration data on a centralized database and two patents on private virtual LANs.

Arista was founded in 2004 in a challenge to Cisco's domination of enterprise networking. It went public shortly before Cisco sued in 2014. Arista's co-founders and its current CEO are former Cisco executives.

Last month, Arista countersued Cisco, charging that the company claims its command-line interface is an industry standard and then tries to punish competitors for using it.

"Our primary focus is the continued supply of products to our customers. We respect the administrative process and the tireless work of the ALJ in this initial determination," Arista said in a emailed statement on Tuesday.